When Manchester United were taken to extra-time in their Carling Cup tie at Crewe Alexandra two weeks ago Sir Alex Ferguson angrily remonstrated with his players and told Kieran Richardson he would be spending time in the reserves. The manager's face was puce and Gary Neville could guess what had happened in the dressing room. "He loses his temper like that about three times a season," said United's captain. "I was watching on television at home and I could see his anger."

Ferguson told the media after Tuesday's fourth-round defeat at Southend that there would be "no suicides or mass sackings" but it is difficult to believe his temper cannot have been pricked again by the manner in which Richardson and fellow B-listers such as John O'Shea and Wes Brown offered the impression of players whose Old Trafford careers were in danger of stagnation.

At intervals Ferguson has spoken of this trio as accomplished performers at the highest level and "the future of this club". The recent evidence, however, is beginning to suggest that all three are heading towards a crossroads that will decide whether they are to remain in the shadows of more senior players or whether, as Ferguson claims, they can establish themselves as first-team regulars in the games that truly matter.

Ferguson's dismay at some of the individual performances at Roots Hall may have been greater than any disappointment about going out of the competition. Richardson, in particular, is a concern at a point in the midfielder's career when his emergence has never materialised as had been anticipated. He, like O'Shea, was indicted by Roy Keane during that diatribe on MUTV 13 months ago and, despite a reluctance to admit as much publicly, people at Old Trafford are bewildered by his lack of progress since he scored twice on his senior England debut against the United States in May 2005.

It seems a long time since Richardson was touted as the possible answer to England's notorious problem position on the left of midfield but, in mitigation, he at least seems to recognise the reasons for Ferguson's disquiet. The player's father recently rang one tabloid newspaper to ask, in a civil fashion, for its reporters not to be too hard on his son. The message was: "He is still young and he knows he has to improve in a lot of areas and work harder."

The case of Brown is particularly intriguing given that he remains a favourite of the Old Trafford crowd and, according to Ferguson, is the "best natural defender in the country". Yet it has become apparent that Nemanja Vidic has overtaken him as Rio Ferdinand's first-choice partner. Brown has undoubtedly suffered from a run of serious injuries but there remains the feeling that he has never quite fulfilled his potential.

The same can be said of O'Shea, who was substituted at Southend and is becoming the player the fans seem to dislike the most. That mantle used to be worn by Darren Fletcher but his form is improving whereas O'Shea's has steadily deteriorated since his breakthrough season. His sympathisers will argue that Ferguson has used him in just about every position apart from goalkeeper and centre-forward. Ferguson has asked him to make central midfield his regular place but it was at full-back that the Republic of Ireland international once excelled.

Overall, Ferguson is entitled to believe his squad is not far off matching Chelsea's for strength in depth - how, for example, would Jose Mourinho compensate for John Terry being injured in February? - but there is obvious cause for concern at Old Trafford about the number of back-up players who seem to be treading water.